Heretofore, as a process for preparing an optically active β-amino acid and its ester by an enantio-selective hydrolysis reaction using a biocatalyst, there has been disclosed a method in which, for example, only one of enantiomers of ethyl 3-amino-3-arylpropionate (racemic mixture) is selectively hydrolyzed in water in the presence of a lipase (trade name: Amano PS) originated from Burkholderia cepacia (Pseudomonas cepacia) to obtain an optically active (S)-3-amino-3-arylpropionic acid and an optically active (R)-ethyl 3-amino-3-arylpropionate (for example, see Non-patent literature 1.).
However, according to this method, there are problems that an E value which is an index of selectivity between enantiomers is low, when an optically active carboxylic acid which is a product is water-soluble, it is difficult to recover 100% of the product from the aqueous solution after completion of the reaction, and yet, under the presence of a large amount of water, lowering in optical purity occurs due to self-hydrolysis reaction of the substrate. Incidentally, the E value is widely utilized as an index of selectivity of kinetic optical resolution (for example, see Non-patent literature 2.).
Also, as a method for obtaining an optically active 3-amino-3-arylpropionic acid, it has been known a method to accomplish a good yield and good optical purity by making an ester portion propyl ester (for example, see Patent literature 4).
However, according to this method, a large amount of water must be used so that there are problems that the operations for the reaction become complicated since it is essential to adjust pH of an aqueous phase, etc. Incidentally, as a required optically active β-amino acid ester, a methyl ester or an ethyl ester thereof is desired in many cases, so that the resulting optically active β-amino acid propyl ester is required to be led to a desired methyl ester or ethyl ester by transesterification, etc., so that this is not an efficient method.
Moreover, as a method for obtaining an optically active 3-amino-3-arylpropionic acid, it has been known a method which can realize high enantio-selectivity by carrying out enzymatic hydrolysis of 3-amino-3-arylpropionic acid ester (racemic compound) in two-phase system of water and an organic solvent (for example, see Patent literature 5).
However, in this method, when an optically active carboxylic acid which is a product is water-soluble, it is difficult to recover the product with 100% from the aqueous solution after completion of the reaction. Also, there was a problem that in the presence of a large amount of water, lowering in optical purity was caused due to self-hydrolysis of the substrate.    Non-patent literature 1: Tetrahedron Lett., 41, 2679 (2000)    Non-patent literature 2: J. Am. Chem. Soc., 104, 7294 (1982)    Non-patent literature 3: “Chemical Dictionary”, Published by Tokyo Kagaku Dojin Shuppan, p. 948 (2000)    Patent literature 1: WO 2004/092116 Publication    Patent literature 2: US 2003/0199692 Publication    Patent literature 3: WO 2001/042192 Publication    Patent literature 4: Japanese Unexamined Patent Publication No. 2003-325195    Patent literature 5: Japanese Unexamined Patent Publication No.2003-325197